scopeofzoology

together broadly

together broadly distinguish the different kinds of animals from each other. Early zoologists dealt only with the description of shapes. It was not until the second and third decades of this century that they turned to the description of sequences of movement, or the 'behavioural structures' of animals. It can be argued that zoology has distinction as a subject only when dealing with the building of three-dimensional shapes, and the assembly of patterns of movement. That is to say, what is distinctly animal is found only in the evolution of communities of cells to form organ systems and the establishment of behavioural structures by which animals interact with each other and with their environment. The motivation of zoologists is summarised by the questions "What is the use in having a particular shape and mode of behaviour? Does it contribute to the animal's success? If so, How?" and "What makes it happen?" Questions on the origins of shape and size are still central to modern zoology. The most original approach to escape the anatomist's method of comparing shapes piecemeal was to view all changes in relative dimensions simply as the topical expressions of some comprehensive and pervasive change of shape through development taking place mainly in one direction. At the turn of the century, D'Arcy Thompson developed this approach to grasp evolutionary transformations as a whole, viewing the change of shape as analogous to that produced by distorting a sheet of rubber on which has been drawn a house or a face. Every single aspect of the drawing changes but the transformation as a whole might be defined by some quite simple formula describing the way the rubber had been stretched. Thompson's methods were later developed by J.S. Huxley into more usable quantitative relationships between the rate of reproduction of one part of the organism to another. This quantification of 8

ideas in comparative anatomy that began in the late l9th century came to an abrupt end at the outbreak of the second World War. In 1945 a new generation of zoologists was in command of research, and it was the comparative experimental approach to physiology that surged forward. The achievements of the D'Arcy Thompson/Huxley school were left behind as a blind end to a particular research philosophy. It is only now, with a marriage between biochemistry and developmental biology that we are beginning to understand the operation of growth mechanisms during development, and to some extent to explain the precise mathematical analyses of the organism in relation to its parts that were carried out between 1900 and 1939. Current approaches to the study of size and shape can be traced to the beginnings of experimental developmental biology. Historically, the study of development as a process began, not with the final product of ontogeny, which was the mainstay of dynastic zoology, but with the developing embryo. In the 1930's experimental embryology had much the same appeal as molecular biology has today, in that students felt it to be the most promising advancing front of biological research. This was partly because histological analysis in early development showed that unity existed between animal dynasties previously separated in terms of gross anatomy. Further, differentiation proceeded uniformly through the mobilisation and deployment of similarly structured cellular envelopes, tubes and sheets in all animals. Chemical unity of evolution was also apparent in the topical organiser theory, which postulated that differentiation in development is the outcome of an orderly sequence of limited but specific chemical stimuli. The underlying assumption of the theory was that an understanding of the chemical properties of the inductive agent would reveal why the amino acid sequence of proteins should differ. Unfortunately the rapid rise of experimental embryology tended to segregate various aspects of the life-cycle as distinct topics within the zoology syllabus, such as differentiation, growth, maturation and ageing, which is only now being overcome. For example, it is currently felt that life should be viewed more as a continuum at the chemical level; ageing and embryonic growth have a unity. 9